It's a good effort.
A few pointers.
1) I'd expect a car promotion like this to be much more panoramic. Effectively your canvas isn't the ideal size. It's a very basic element of design but one that is often overlooked.
2) It looks like you've added on the photos, logo and text after designing the background. They don't integrate or complement each other. I understand you want them to stand out, but a more subtle effect is needed. To be honest, I'd drop the photos altogether, make the logo smaller and give it some blending.
3) Using handwriting to feel personal does work, but not if you've lumped it in with some Sans. Your text really contrasts and doesn't sit well in the frame. Try taking it off white and bring some of your other colour into it, maybe where you have the split gran/cabrio. Try making grancab bigger too and possibly split the phrase onto two lines so that it's justified.
4) The background works quite well, I'd say the left background mountain needs tweaking. It needs to be smaller as it currently detracts from the impression of distance. I'd bring the comet trail above the vignette too, which can act as a lead in to the piece.